Angiogenesis is a process that involves the recruitment, replication and migration of endothelial cells and is pivotal for the survival of the surrounding tissue during development, would healing, reproductive cycles and tumor development. One grown factor that plays a pivotal role in these events is basic fibroblast growth factor (FGF-2). FGF-2 is synthesized as 24, 22.5, 22(hmwFGF-2), and 18 kD forms with the 24 kD FGF-2 containing a 55 amino acid extension at the amino terminal end (ATE) of 18 kD FGF-2. While 18 kD FGF-2 stimulates endothelial cell migration, we have found that hmwFGF-2 inhibits is. This inhibitory activity is effective in the presence of 18 kD FGF-2 and VEGF, another stimulus of enhanced migration. HmwFGF-2 also inhibits migration of mammary carcinoma cells (MCF-7) responding to insulin-like growth factor 1. Antibodies generated against an 12 amino acid fragment of the ATE block the inhibition of migration but antibodies to the 18 kD FGF-2 have no effect. HmwFGF-2 stimulates proliferation of MCF-7 cells but this activity is not blocked by the antibodies against the ATE but is reversed by anti-18 kD FGF-2 antibodies. Thus, the inhibition of migration is a function of the ATE while the effect on growth rate is promoted by the carboxy terminal 18 kD FGF-2. In addition, studies examining the intracellular mechanism that mediates hmwFGF-2 inhibition of migration clearly show that the estrogen receptor (ER) is involved; elimination of the ER from either endothelial or MCF-7 cells abrogates the inhibitory response (without affecting the growth stimulatory effect) and treatment with hmwFGF-2 leads to enhanced phosphorylation of the ER. Thus, we propose that the ER plays a pivotal role in this process. This grant proposal will address the mechanism by which hmwFGF-2 (presumably the ATE region) inhibits migration of endothelial and breast tumor cells. The hypothesis states that hmwFGF-2 binds to FGF receptors distince from 18kD FGF-2 binding, that this effect is mediated exclusively through the ATE region of hmwFGF-2, and is mediated intracellularly through an ER- dependent pathway. The experiments will examine the mechanism by which hmwFGF-2 inhibits mitogen-stimulated migration considering receptor binding and activation, intracellular pathways, as well as cytoskeletal arrangement. This study addresses a novel and unique role for FGF-2 in tumor development and possibly metastasis, the regulation of cell migration by hmwFGF-2.